It is known in the art of indicia reading terminals (e.g., bar code readers) to process a plurality of successively captured setup frames of image data prior to subjecting a captured frame of image data to a decode attempt. In typical operation of a commercially available bar code reader, a plurality of setup frames may be successively captured and subject to processing for exposure period parameter determination. For determining an exposure parameter, a set of pixel values of a frame corresponding to a predetermined spatial distribution pattern (e.g., evenly distributed or weighted toward centered pixel portions) may be averaged for determination of a frame white level. The white level determined using pixel values taken from the predetermined distribution pattern is compared to a target white level. The exposure period may be increased if the white level is lower than the target level, and decreased if the white level is higher than the target white level.
The prior art approach to parameter development has been observed to result in misreads and long trigger to read (TTR) times in indicia reading terminals. Misreads are particularly common using the prior art approach where a captured image representation includes large white areas outside of a decodable indicia region of an image representation, or large dark areas outside of a decodable indicia region of an image representation.